1. Field of the Invention
The present invention relates to novel esterified carboxymethyl celluloses soluble in organic solvents. More particularly the invention relates to novel esterified carboxymethyl celluloses soluble in organic solvents, having a degree of substitution by carboxymethyl group of 2.00 or more and a degree of substitution by an esterified carboxymethyl group of 1.50 or more.
2. Brief Description of the Prior Art
Carboxymethyl cellulose (hereinafter abbreviated as CMC) is an cellulose ether which is prepared by reacting cellulose with monochloroacetic acid in the presence of alkali. It is a water-soluble high molecular electrolyte widely used as viscosity-increasing agent, dispersing agent, protective colloid, adhesive or the like. As CMC those having a degree of substitution (hereinafter abbreviated as DS) by carboxymethyl group of 0.5 to 1.7 are popular, and they are commercially available usually in the form of sodium salt and partly in the form of ammonium salt or calcium salt. The calcium salt is insoluble in water and it is used mainly as disintegrator. Thus CMC is used as a water-soluble high molecular electrolyte for various purposes. However, such known CMCs have a big defect that they are hardly soluble in any organic solvent.
As a method of making CMC soluble in organic solvents, there can be considered a process of converting it into an esterified CMC by reacting the carboxymethyl groups of CMC with an alcohol, an alkyl halide, an epoxy compound or the like. By esterification of commercially available CMC harving a DS less than 2.00, however, any esterified CMC soluble in organic solvents was not prepared. The product obtained was slightly swollen and hardly dissolved in organic solvents. Although there can be mentioned Japanese Patent Publication No. Sho 45-36143 and Japanese Laid-open Patent No. Sho 49-18981 as examples of the preparation of an esterified CMC, the products disclosed there are both a water-soluble esterified CMC.